I. Field of the Invention
The present invention relates generally to the field of acoustics, and more particularly, to a three dimensional microphone apparatus and system and a three dimensional hearing aid.
II. Description of the Related Art.
FIG. 1 illustrates a perspective view of a prior art “In The Ear” (ITE) hearing aid 100. This typical hearing aid 100 includes a central body 105 having a general shape that is adapted to fit into a user's ear canal. The rear-most portion 110 is adapted to fit into the canal closest to the ear drum and includes a speaker 115. The forward-most portion 120 typically protrudes or is flush with the opening of the user's ear. The forward-most portion 120 includes a face 125 that includes operational features of the hearing aid 100. These features include a microphone element 130 that is adapted to receive acoustical spectra (sounds) from the environment. The microphone element 130 is typically placed underneath the surface of the face 125 flush with the outer surface shell and an opening 135 allows the sounds to enter to the microphone element 130. In general, the microphone element 130 is of the type having a microphone membrane facing outward from the hearing aid. The other operational features of the hearing aid 100 typically include a battery door 140 behind which a battery (not shown) can be placed to operate the inner electronics (not shown) of the hearing aid 100. These electronics typically process and amplify the received sound for transmission to the speaker 115 so that a user can hear the received sounds. The operational features further include a volume control 145 and a micro-handle 150 so that the user can easily place and remove the hearing aid with the use of finger tips. It is understood that there are many different variations in the type of hearing aids presently available. The hearing aid 100 is shown for illustrative purposes.
Microphone elements 130 in typical hearing aids such as hearing aid 100 suffer from several disadvantages. These disadvantages primarily include pre-eminence and proximity effects. In general, human hearing is three dimensional. Typical listeners with normal hearing can discern the location of several sounds and can also discriminate between sounds when there are a large number of sounds in a given area. However, with a typical hearing aid, pre-eminence is the effect in which the loudest sound near the microphone element in the hearing aid is the dominant sound, drowning out other sounds, particularly those sounds farther away from the microphone element. Sounds are therefore positioned by loudness and frequency so that the listener can not discern how far apart different sounds are from one another. In essence, sound becomes two-dimensional instead of three-dimensional.
Another disadvantage to microphone elements 130 in typical hearing aids is proximity effects. A typical proximity effect occurs when the microphone element is brought near a reflective boundary, for example, a telephone handset. The proximity effect affects the frequency response of the microphone element in the hearing aid thereby creating phase problems and potential feedback in the system.
In general, another disadvantage of modern hearing aids is that they include microphone elements that have a cardioid pattern. A cardioid pick-up pattern can only pick up sounds most efficiently when they are directly perpendicular to the microphone. The more a sound source moves away from a direct path, the more the microphone loses the ability to pick up that sound.
A further disadvantage of typical hearing aids is that background noise appears to have the same dominance as desired target sounds.
Still another disadvantage with a typical hearing aid is that the microphone element is mounted underneath the face (see 125 above) of the hearing aid and is provided a small opening (see 135 above). Therefore, the membrane has a diameter larger than the opening. This orientation of the microphone element further detrimentally effects the frequency response of the hearing aid. Since hearing aid transducers are small, the frequency response is detrimentally affected.
Many of these disadvantages are due to the microphone technology utilized in the hearing aids. In order to overcome the disadvantages of microphones, several approaches have been taken. For example, U.S. Pat. No. 4,361,736 provided a process and apparatus transducing acoustical signals without discrimination between direct and random incidence acoustical variations of the sound being transduced., typically within a desired frequency range. These advantages are attained by affixing a boundary in front of a microphone element, thereby creating a pressure zone between the boundary and the microphone element. The process and apparatus helped reduce or eliminate the discrimination between the frequency spectra of direct and random incidence sound waves in a frequency of interest and the lack of the ability to reject undesired high frequencies that can cause unwanted pressure build-up at the microphone, among other problems. This frequency range could be mechanically determined by the spacing between a boundary and an acoustically isolated microphone element, which determined high frequency cut-off, and the size of the boundary, which determined low frequency cut-off.
Other technologies using “boundary layer” microphones typically provide a large boundary in which a microphone element is mounted within and flush with the boundary. In theory, the sound waves (typically the perpendicular components) incident on the boundary are superimposed in phase thereby essentially doubling the acoustical pressure which increases the sensitivity, typically by 6 dB, of the microphone mounted on the boundary. The doubling of the acoustic pressure typically occurs best where the boundary surface is large compared to the wave length of the sound waves.
The problems with these associated technologies results from the fact that large boundaries are needed to obtain good low frequency response. Furthermore, many microphone technologies to improve frequency response are not utilized in hearing aids due to the miniaturization problem.